Electric current collecting element



Dec. 6, 1966 R. H. SAVAGE ELECTRIC CURRENT COLLECTING ELEMENT Filed June21. 1965 /n van/0r Haber) H. Savage,

His Afro/06V- United States Patent 3,290,472 ELECTRIC CURRENT COLLECTINGELEMENT Robert H. Savage, Scotia, N.Y., assignor to General ElectricCompany, a corporation of New York Filed June 21, 1965, Ser. No. 465,556Claims. (Cl. 200-166) This invention relates to contact elements for thecollection and delivery of current in electrical devices both by themechanism of make-and-break contact and by sliding contact.

Contact carbon brushes for the collection and delivery of electricalcurrent are most commonly employed, because of the natural lubricatingqualities thereof. However this material, usually graphite, has thedisadvantage .that it is quickly subject to substantial wear in use andalso shows higher electrical contact resistance than do the metalscopper, silver, gold, palladium and platinum. Various attempts have beenmade to offset the abnormal wear of carbon brushes by impregnatinggraphitic carbon with inclusions of metals (i.e. copper or silver), bythe addition of solid lubricant materials (i.e. molybdenum disulfide),and by the incorporation of organic compounds into the contact body. Thepurposes for the various modifications to carbon brushes differ, but allachieve substantially the same object; to wit, reduction of the wearrate. This reduction may be effected either through direct lubricantaction or by reduction of electrical erosion through improved currentconduction.

Metal contacts used either as make-and-break elements or as slidingconductors have the disadvantage that, because the contact isunlubrioated, consequent welding occurs between the contact element andthe surf-ace. Also lack of lubrication may lead to arcing, which in turncreates regions of roughness in the metal surface, thereby precipitatingfurther arcing in an autodestructive manner. Metal contact elements,while they are operating satisfactorily, have the distinct advantage ofbeing excellent conductors of electricity.

Therefore, it is the prime object of this invention to provide acomposite contact element combining the advantage of both metalconstruction and lubricant construction.

It is another object of this invention to provide a contact elementusable either in a make-and-break electrical current-carrying capacityor as a sliding contact, the construction thereof combining a highlyeffective electrical conductor in the form of .a metal shell having acore consisting of a low adhesion electrically conductive material,which will neither stick to the surface from which current is beingcollected by sliding contact nor evaporate or splash under the difficultelectrical disturbances characteristic of the make-and-break processes.

It is still another object to provide a composite makeand-break contactelement having a metal outer wall and a core of electrically conductinglubricant material disposed to make contact (on closing) with a movableportion of a juxtaposed contact surface, whereby after an initialcontact is made with the conducting lubricant core, the dwell period ofthe electrical contact occurs with contact between the metal portion ofthe contact surface and the metal wall of the composite element.

These and other objects may be attained in the practice of thisinvention by the construction of small metal contact elements having alarge portion of the cross section thereof composed of an electricallyconducting lubricating material. The construction can be effected eitherby providing -a recess in a metal contact, which recess is then providedwith the lubricant core by pressing a rod of the lubricant materialtherein, or by a more commercially practical method; that is, filling ametal cylinder 'ice with the electrically conducting lubricant corematerial, plugging the ends of the cylinder, swaging the composite to areduced diameter, and then finally, drawing the structure into smallwire of the requisite composite cross-section. Once drawn into wire itis expedient to cut the wire in appropriate lengths as required. Themore common metals to be employed as the thin outer contacting wall ofthe composite construction are copper and silver, alalthough othermetals may be employed. The contacting core material may, for example,be graphite, molybdenum disulfide (modified to render it electricallyconductive), mixtures of silver and graphite.

The exact nature of this invention will be more readily apparent fromconsideration of the following specification relating to the annexeddrawing in which:

FIG. 1 is a small composite contact button having a metal wall and agraphite core;

FIG. 2 shows a short length of composite wire construction having abevelled contact face;

FIG. 3 composed of FIGS. 3a, 3b, and 3c schematically illustrates stepsof production by which the composite wire construction shown in FIG. 2may be produced;

FIG. 4 schematically illustrates the use of the contact element shown inFIG. 1 as a make-and-break element, and

FIG. 5 shows the application of the composite structure shown in FIG. 2in conjunction with a timing disk employed as a motor control.

Thus, to describe in greater detail the invention illustrated in thedrawings, the small composite contact button 10 shown in FIG. 1 wasconverted from a metal contact button by providing recess 11 therein andthen force-pressing tight-fitting carbon rod 12 into the recess. As aresult a composite construction having a cross-section is producedcontaining a large percentage of low adhesion material to serve in therequisite lubricant capacity for the metal shell disposed in contactwith the surface from which current is being collected. The action offorcing the tight-fitting graphite rod 12 into the recess 17 insures agood electrical contact between the graphite core and metal shell 13. Asindicated above, the metal wall 13 is preferably constructed of copperor silver, although other metals or alloys may be employed.

Similarly in FIG. 2 the composite current collecting wire element 16consists of metal wall, or shell, portion 17 serving as a goodelectrical conductor and enclosing the sidewall area of the electricallyconductive lubricant core 18. Another particularly important advantageof employing metal as the outer wall consists in the ease With whichattachment can be made thereto by mechanical means, as by soldering orwelding. The outside diameter of the wire is, of course, a matterdepending upon the particular application; however, wire sizes in therange of from about 10 to 60 mils are suitable for the practice of thisinvention. Preferably, the ratio of the radius of the lubricant core tothe thickness of the metal wall will be within the range of from about20:1 to 1:1. Expressed another way, the ratio of the cross-sectionalarea of the lubricant core to the cross-sectional area of the metal wallwould be in the range of from about 400:1 to 1:1.

The choice of the core material to be used is controlled by relativelysimple criteria. Thus, the core material must be free of corrosiveimpurities (nor may it itself be corrosive) such as will causedeterioration of the metallic wall portion enclosing it; the corematerial in its compacted state should have a coefiicient of frictionagainst itself or against copper or silver of less than about 0.5(preferred range about 0.05 to about 0.25), and it should haveelectrical resistivity of less than 10 ohm-centimeter.

Examples of core materials meeting these criteria are graphitic carbon,graphitic carbon mixed with silver or copper, graphitic carbon mixedwith solid lubricants, such as molybdenum or tungsten disulfide, andelectrically conductive molybdenum disulfide or tungsten disulfide.

Referring to FIG. 3, process steps for preparing the composite wireelement shown in FIG. 2 are illustrated. First, a tubular body or billet20 (FIG. 3a) is prepared comprising tube 21, filled with compressedpowder, or granular material 22, to form a core. The filler material, asfor example graphite, is retained within tubular body 20 during thesubsequent swaging and drawing operations by the end caps or plugs 23,24, which are welded (or otherwise fixedly secured) to tube 21. Thebillet 20 is next swaged to drawing size, after which the composite bodyof reduced diameter so produced is subjected to successive wire drawingstages as shown in FIGS. 3b and 3c to produce composite wire of theultimate small diameter. In reducing the tube and its core from itsoriginal size to wire size, approximately a 90% reduction in size mayadvantageously be employed. Then, the composite wire so produced may becut into such varied lengths as may be required.

As an illustration of the manner in which the composite contact elementsforming this invention may be employed, reference is made to FIGS. 4 and5. Thus, in FIG. 4 a make-and-break device is shown employing thecontact button element shown in FIG. 1 afiixed to flexible spring-likearm 31. Motor panel 32 is activated in response to the demands of timermechanism 33, such as may be employed in an automatic washing machine.Timer 33 receives power from the l10-volt power source, which servicesmotor panel 32. Upon demand from timer 33 solenoid 34 is actuatedpulling the flexible member 31 toward it. During this movement core 12of element 10 contacts the depressible contact 36 of a stationarycontact forcing contact 36 inwardly against the action of spring 37,which is located in recess 38 of metal stationary contact 39. In thismanner initial electrical contact (making) occurs between core element12 and depressible contact 36. Thereafter, as contact 36 is forcedinwardly, the annular metal portion 13 of composite contact element 10,which encloses core 12, is brought into contact with the face ofstationary contact 39. Because of its lower electrical resistance thismetal shell then assumes the function of conducting most of the currentthrough the switch. With the make-andbreak switch closed the requisitepower is provided to motor panel 32. As dictated by timer 33, breakingof the circuit occurs with the annular metal portion 13 of compositecontact element 10 moving away from the face of stationary element 39without causing arcing, because of the continued electrical contactbetween core 12 and depressible element 36. By the use of suchconstruction, it is possible to employ the core 12 to effect themakeand-break functions, while the dwell time of switch closure occurswith metal-to-metal contact.

The structures shown in FIGS. 1 and 2 are interchangable for the purposeof collecting current and it is to be understood that applicationsillustrative of the one structure are also illustrative of the other.

In FIG. 5, by way of example, the rotating disk 41 schematicallyrepresents part of a timing mechanism such as is conventionally employedin an automatic washer (not shown). The composite wire contact elementillustrated in FIG. 2 is shown in juxtaposition to rotating disk 41.Sliding contact element 42 is held in fixed position so that, as disk 41rotates, the timing islands 43 are brought into contact with element 42.The disk 41 is itself electrically nonconductive, while the timingislands 43 are electrically conductive. The arc length of the individualislands 43 in conjunction with the rate of rotation of disk 41determines the period of time during which some given automaticoperation is conducted by the machine, because of the completion of anelectric circuit through ring contact 44, lead 46, the particular island43 and the sliding contact 42. Interruptions in motor operation occurwhen the electrically nonconducting portions of disk 41 are rotated intojuxtaposition with the sliding contact elements 42.

The use of the composite construction illustrated in FIG. 2 anddescribed herein is of particular advantage because of the dual functionexercised thereby. Because of the lubricating capacity of the core andits capacity for electrical conductivity it becomes feasible to employthe metal wall, which surrounds the core and provides structuralintegrity to the composite, in direct electrical contact with thesurface thereby to more elfectively collect current therefrom.

Thus, by the use of the structures illustrated and described herein, anovel construction for a contact element has been provided and, inaddition, processes for the production thereof. By successfullycombining the necessary materials for the simultaneous exercise oflubrication and superior electrical conduction, the resultingconstruction is one of substantial utility. Obviously, modifications ofthe materials employed for the core and metal wall are possible in thelight of the above teachings. It is therefore to be understood thatwithin the scope of the appended claims the invention may be practicedotherwise than as specifically described.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A longitudinally-extending electric current collecting element havingan exposed current collecting contact face, said element comprising:

(a) a longitudinally-extending core of low adhesion,

electrically conducting material, and

(b) an outer longitudinally-extending wall of metallic material havinglow electrical resistance enclosing said core over the sidewall areathereof,

(1) said element having as an exposed current collecting contact face anarea of said low adhesion material surrounded by an area of saidmetallic material with the ratio of the area of low adhesion material tothe area of metallic material being in the range of from about 400:1 to1:1.

2. A current collecting element substantially as recited in claim 1wherein the low adhesion material contains graphite.

3. A current collecting element substantially as recited in claim 1wherein the low adhesion material contains a solid lubricant.

4. A current collecting element substantially as recited in claim 1wherein the element is substantially cylindrical in configuration.

5. In a make-and-break switch for selectively interrupting andpermitting the passage of electric current by the separation andapproximation of first and second opposed, relatively movable contacts,the improvement comprising: (a) the first contact having a currentcollecting contact face comprising a concentration of low adhesion,

electrically conducting material circumscribed by a metallic rim havinglow electrical resistance with the ratio of the contact face area of lowadhesion material to the contact face area of metallic material being inthe range of from about 400:1 to 1:1, and

(b) the second contact having a portion thereof movable relative to thebalance of said second contact and projecting toward said first contact,

(1) said moveable portion and said balance of said second contact beingmade of electrically conducting material and being in direct physicalcontact with each other,

whereby as said contacts are brought into juxtaposition, said lowadhesion material forms an electrical contact with said movable portionbefore said metallic rim comes into contact with said balance of saidsecond contact.

6. The improvement in make-and-break switches substantially as recitedin claim 5 wherein the low adhesion material contains graphite.

7. The improvement in make-and-break switches substantially as recitedin claim 5 wherein the low adhesion material contains a solid lubricant.

8. In an electrical current transmitting juncture comprising first andsecond juxtaposed contacting surfaces, said first surface being thecurrent collecting face of a longitudinally-extending current collectingelement and said first and second surfaces being adapted for movementrelative to each other, the improvement wherein:

(a) the collecting element comprises a longitudinallyextending core anda longitudinally-extending metallic shell,

(1) said core containing a concentration of low adhesion, electricallyconducting material,

(2) said metallic shell enclosing said core over the longitudinal wallarea thereof, having low electrical resistance and having a maximumvalue for the cross-sectional wall area about equal to thecross-sectional area of said core, and

References Cited by the Examiner UNITED STATES PATENTS 1,986,222 1/1935Sachs 200l66 2,499,420 3/1950 Sakatos 200166 2,888,740 6/1959 Danis29420 References Cited by the Applicant UNITED STATES PATENTS 2/1948SaWhill. 6/1959 Danis.

ROBERT K. SCHAEFER, Primary Examiner.

H. O. JONES, Assistant Examiner.

1. A LONGITUDINALLY-EXTENDING ELECTRIC CURRENT COLLECTING ELEMENT HAVINGAN EXPOSED CURRENT COLLECTING CONTACT FACE, SAID ELEMENT COMPRISING: (A)A LONGITUDINALLY-EXTENDING CORE OF LOW ADHESION, ELECTRICALLY CONDUCTINGMATERIAL, AND (B) AN OUTER LONGITUDINALLY-EXTENDING WALL OF METALLICMATERIAL HAVING LOW ELECTRICAL RESISTANCE ENCLOSING SAID CORE OVER THESIDEWALL AREA THEREOF, (1) SAID ELEMENT HAVING AS AN EXPOSED CURRENTCOLLECTING CONTACT FACE AN AREA OF SAID LOW ADHESION MATERIAL SURROUNDEDBY AN AREA OF SAID METALLIC MATERIAL WITH THE RATIO OF THE AREA OF LOWADHESION MATERIAL TO THE AREA OF METALLIC MATERIAL BEING IN THE RANGE OFFROM ABOUT 400:1 TO 1:1.